In a wireless communication system such as a Wideband Code Division Multiple Access (WCDMA) by Third Generation Partnership Project (3GPP), a Long Term Evolution (LTE), a LTE-Advanced (LTE-A), a Wireless LAN by The Institute of electrical and Electronics engineers (IEEE), and Worldwide Interoperability for Microwave Access (WiMAX), a base station (a cell, a transmission station, a transmission device, and an eNodeB) and a terminal (a mobile terminal, a reception station, a mobile station, a reception device, and a User Equipment (UE)) respectively include a plurality of transmitting-receiving antennas, thereby it is possible to realize high-speed data transmission by a Multi Input Multi Output (MIMO) technology.
In such a wireless communication system, a channel state between the base station and the terminal is measured by using a reference signal for measuring the channel state (Channel State Information-Reference Signal (CSI-RS), a pilot signal, a known signal) configured by signals that are commonly known between the base station and the terminal. Further, in the wireless communication system, a Modulation and Coding Scheme (MCS), a spatial multiplexing number (number of layers and rank number), a precoding weight (precoding matrix and precoder), and the like are adaptively controlled based on the measured result, thereby it is possible to realize more efficient data transmission.
Further, in a case where the base station transmits data signals to the terminal, demodulation reference signal for the data signal (Demodulation Reference Signal (DMRS) and UE-specific RS) configured by the signals that are commonly known between the base station and the terminal are multiplexed and transmitted. The demodulation reference signal for the data signal may be multiplexed into the data signal, prior to performing a precoding process with respect to the terminal. Therefore, the terminal may measure the precoding process performed by the base station and equalization channel including a channel state, by using the demodulation reference signal for the data signal. For example, a method described in NPL 1 may be used. Accordingly, the terminal may perform a demodulation process of the data signals transmitted by the base station, even without knowing the precoding process performed by the base station.
On the other hand, it is possible to build a wireless communication system using a heterogeneous network configuration by a macro base station having wide coverage and an RRC (Remote Radio Head) having narrower coverage than the macro base station. FIG. 13 is a schematic diagram of the wireless communication system using the heterogeneous network configuration. In an example shown in FIG. 13, the heterogeneous network configuration is formed by a macro base station 1301, an RRC 1302, and an RRC 1303. The macro base station 1301 builds coverage 1305, and the RRH 1302 and the RRH 1303 respectively build coverage 1306 and coverage 1307. Further, the macro base station 1301 is connected to the RRH 1302 through a line 1308, and connected to the RRH 1303 through a line 1309. Thus, the macro base station 1301 may transmit and receive a control signal and a data signal with the RRH 1302 and the RRH 1303. The line 1308 and the line 1309 may use a wire line such as an optical fiber or a wireless line using a relay technology. In this case, all or a part of the macro base station 1301, the RRH 1302, and the RRH 1303 respectively use the same frequency (resource), thereby it is possible to improve an overall frequency usage efficiency (transmission capacity) within an area of the coverage 1305.
When the terminal 1304 is located within the coverage 1306, the terminal 1304 may perform a single cell communication with the RRH 1302. Further, when the terminal 1304 is located around the edge (cell edge) of the coverage 1306, it is necessary to take measures against co-channel interference from the macro base station 1301. A method is considered which reduces or suppresses the interference to the terminal 1304 in a cell edge area, by performing an inter-base station cooperative communication in which adjacent base stations cooperate with each other, as a multi-cell communication (cooperative communication) between the macro base station 1301 and the RRH 1302. For example, in NPL 2, a Cooperative Multipoint (CoMP) transmission scheme is considered as such a scheme.